This invention relates to protecting a splice of multiconductor electrical cables from the ingress of water. Of particular interest are communication cables, such as telephone cables.
The multiconductor communications cables usually comprise a core containing a plurality of individually insulated wire conductors surrounded by an outer sheath. The cable core may contain a few pairs of conductors up to several hundreds or even thousands of pairs of conductors. The outer sheath of the cable usually is a plastic jacket surrounding a metal shield. Additional inner polymeric layers may be present. The cables are usually referred to as "filled" cables because the cable is usually filled with a filling compound such as a grease or petroleum jelly which helps prevent the ingress of water into the cable.
When two or more of the cables are spliced together, the jacket and other layers of the cable are removed near the end of the cable to expose the individual insulated conductors which are then individually connected to the conductors from the other cable or cables. After completion of the splice the entire splice area must be protected from ingress of water. Various devices and methods have been used for protection of such splices such as U.S. Pat. Nos. 3,361,605 to Gilbert, 3,895,180 to PIummer, and 3,992,569 to Hankins et al. Plummer and Hankins are typical examples of methods and apparatus used to protect cable splices of the type referred to above and are sometimes referred to as "buried splice closures." These types of cables are commonly used underground and the splices must be protected to prevent ingress of water when they are buried underground.
It is generally recognized that one of the paths through which water may enter the splice area and damage the individual spliced conductors by corrosion or short circuit is by migration through the interior of one or more of the cables spliced. Since such water migration occurs in the "filled" cables, it is necessary to provide splice protection method and apparatus to prevent water from entering the splice area from any path, including through the interior core of the cable. U.S. Pat. No. 4,466,843 to Shimirak recognized the importance of applying pressure to the liquid sealant while the liquid sealant cures to form a water impenetrable seal.
The liquid sealants used to protect splices of the type referred to herein are generally curable liquid polymer systems which comprise a prepolymer and a curing agent or hardener which can be mixed together and poured into the splice enclosure and allowed to cure. Particularly useful curable liquid sealants are the two-part polyurethane systems. The sealants normally used solidify to a gel-like consistency, i.e., the solid cured sealant has considerable elasticity to allow the sealant to conform to changes in size or shape of the splice area due to expansion or extraction or other mechanical forces acting on the splice area. These sealants are also usually reenterable.
U.S. Pat. No. 3,639,567 to Hervig discloses the use of expanding foams to form cable blocks. In this application it appears important that the viscosity of the material increase to a fairly high level before the expansion of the material begins. It also appears important that the expansion of the material not exceed about 25 percent in volume.